So my online therapist gave me an awesome strategy to use when you feel derealization coming on. For me, it stops it almost right away. I hope it comes in handy for others:
"When you feel yourself depersonalizing, look around and see three things present where you are, naming them. Name specific things, in detail, as you see them. For example, I see a picture of my old dog with a wet nose; I see a black computer speaker; and so on. Then name three things you can hear, like the humming of a fan, cars passing by, the dishwasher running, and so forth. Then name three things you can feel through the sense of touch. I feel the jeans against the skin of my left thigh; I feel the soles of my feet on the floor, and so on. If you get stumped, it’s ok to repeat things, just concentrate on actually sensing them in the present moment. Then repeat the whole process - for sight, hearing and touch - for two things each, and then one thing for each."
I don't do it as many times as he tells me to, but I notice it really helps bring me back to the real world even if I just focus on sounds, or things that I see.
Take care, guys x